FD standard manual Diff 7800 rpm, 17 inch wheels with 50 profile tyres.
also whats the formula to work it out?
Hypothetical obviously:Ladys-man
FD3s standard manual diff ratio: 4.1:1 FD3s standard gearbox ratios: 1st 3.483:1
2nd 2.015:1
3rd 1.391:1
4th 1.000:1
5th 0.719:1 17 inch wheels with 50 profile tyres: Width is important here as the 50 profile refers to the sidewall height relative to the tread width. For now I\'ll presume a width of
265, giving a rolling diameter of
695.8mm and a circumference of
2.18m (0.00218km). ----------------------------
Ok, now we have all the numbers we need. The maths goes as follows:
(((Engine RPM/Gearbox Ratio)/Final drive ratio)*60)*Driven tyre circumference=Ground speed in KPH.
Multiply by 0.62137 to show the KPH value in MPH.
----------------------------
Using the numbers you provided:
(((
7800/
0.719)/
4.1)*60)*
0.00218 =346.090kph *0.62137
=215.04mph
that seems far to fast for stock fd box dont it :|
Yeah way too fast, i thought it would be 170ish
nah i think it will be a bit faster, i member going 165 at 6800, clocks and power fc might be out though!
i dont see how tread width is important, i think the circumference of the tyre is wrong
what am i saying its only 1k more lol!
From the 200mph build thread they guy has to do 9020 rpm to hit 200 dead, on a auto diff
tread width is important because the aspect ratio eg, 50 like in your case, is 50% of the height of the width...
so a 265/50, is taller than a 255/50.
oh right, hmmmm thats interesting, so im looking at 165mph at 6800?
i am 90% sure thats what mine was around!
The single biggest factor in producing that huge calculated speed value is the huge height (or radius - I use the term height because that\'s how race car tyres are numbered) those 50 profile tyres have.
A 50 profile 265 equates to a height of 695mm(!) As a comparison on my race car I run 285/650 rears. 695 is as tall as a skyscraper, is it a drag tyre or maybe borrowed from a rear-engined Porsche..? On 650 rears at 7800 rpm an FD3s using a standard drivetrain would be travelling at 179 mph.
If this is a real car in question and not a hypothetical one, I seriously suggest running much lower profile rear tyres unless there\'s a darn good reason for those tractor boots!
ok guys, ill help you out with this.
assuming 4.1 diff at 7800rpm
235/50/17 181mph
245/50/17 184mph
255/50/17 187mph
265/50/17 189mph
275/50/17 192mph
this makes the assumption that the tyres are new and havent been worn down, the more used(less tread) the slower you are going at a set rpm
most people run 255/40/17 ont he back of there rx7, with a stock diff you need to hit 9020rpm to do 200mph, with an auto diff you need 8580rpm
If you want to know exactly ill need either the diameter or the circumference of your current tyres
I have just measured the diameter its 626mm (oh and they are 255/40/R17) oooops.
Can you do a little list of speeds for that matey
172 mph i think.
Quote from: DR SCHNITZEL;682735I have just measured the diameter its 626mm (oh and they are 255/40/R17) oooops.
Can you do a little list of speeds for that matey
ok on brand new 255/40/17
6000rpm 133mph
6500rpm 144mph
7000rpm 155mph
7500rpm 166mph
7800rpm 173mph
8000rpm 177mph
on your used tyres
6000rpm 131mph
6500rpm 142mph
7000rpm 153mph
7500rpm 164mph
7800rpm 170mph
8000rpm 174mph
if you have any other rpms, diff/gearbox ratios and tyre sizes let me know.
If you also want to give me a horsepower assuming your on a stock body i can tell you roughly what speed you will hit within 1.5miles and also with unlimited distance
Ok mate lets say i have about 420 at the hubs, t04r at 1 bar standard ports. i have taken about say 60 kilos out of the car
post up the formulas
Turbotoaster, none of your calculations make sense according to the numbers I have.
What are you using as 5th gear ratio in your calculations?
According to the info I have internal gearbox ratios are as follows:
1st - 3.483:1
2nd - 2.015:1
3rd - 1.391:1
4th - 1.000:1
5th - 0.719:1
Which on new 255/40/17 would in 5th gear give:
6000rpm 153mph
6500rpm 166mph
7000rpm 179mph
7500rpm 191mph
7800rpm 199mph
8000rpm 204mph
Quote from: DR SCHNITZEL;682748Ok mate lets say i have about 420 at the hubs, t04r at 1 bar standard ports. i have taken about say 60 kilos out of the car
First thing I\'ll say is that weight has no direct impact on terminal velocity (when power is equal to drag) only by the amount it\'s pressing the tyres into the ground, causing friction. Weight affects acceleration but at terminal velocity there is no acceleration.
I\'ll have to think about calculating this one as it means rearranging a couple of big equations.
One other value will be needed - the frontal area of an FD.
Quote from: DR SCHNITZEL;682748Ok mate lets say i have about 420 at the hubs, t04r at 1 bar standard ports. i have taken about say 60 kilos out of the car
Ok assuming you had perfect gearing and unlimited distance it would be possible to hit 197mph, but we are talking bonnieville type setup or the place that VW use.
if we say 1.5miles then your looking at 177mph with perfect gearing, since that isnt normally possible, it all depends on where your making max power and how much it drops off after peak power.
say for example you made 420 at 8krpm, that would be perfect for you 1.5mile run as at max speed your making max power.
if for example you made 420 at 7krpm and 370 at 8k then you would find your losing power when you need it the most and your top speed would be less, say 173mph
Quote from: raceralexuk;682766Turbotoaster, none of your calculations make sense according to the numbers I have.
What are you using as 5th gear ratio in your calculations?
According to the info I have internal gearbox ratios are as follows:
1st - 3.483:1
2nd - 2.015:1
3rd - 1.391:1
4th - 1.000:1
5th - 0.719:1
Which on new 255/40/17 would in 5th gear give:
6000rpm 153mph
6500rpm 166mph
7000rpm 179mph
7500rpm 191mph
7800rpm 199mph
8000rpm 204mph
Yes it looks like you cant understand it because the 5th gear ratio is actually wrong, its actually 0.820:1 for some reason the 5th gear was published wrong which is why alot of people think they are going faster than they actually are.
The ratio I use is something i worked out and tested myself and its spot on, so you wont find that ratio anywhere online though.